Indeed, there are various
types of
exotic compact objects (ECOs) [1]}, [2]}, [3]} proposed
that are claimed to mimic BHs in these binaries.
However, incorrect inferences about their true nature can have far-reaching implications, such as on population models of compact objects.
In the future, the proposed 3rd generation ground-based GW detectors Einstein Telescope [4]} and Cosmic Explorer [5]} are expected to have order-of-magnitude better sensitivity compared to current ones in estimating the source parameters, which should enable us to probe
the
nature of these objects more
accurately.
Multiple models of ECOs have been proposed, including
Planck-scale modifications of BH horizons [6]}, [7]}, gravastars, [8]}, and
boson stars [9]}, among others. Building separate models for each of these exotic objects is a hard
problem, and accurate measurements of their properties are not yet possible with the current detectors. So, a more practical
approach would be to devise tests that are generic and
model-independent and are based on our understanding of
binary black hole dynamics.
